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911.
Alan Bruce Thompson 《Contributions to Mineralogy and Petrology》1971,33(2):145-161
Equilibria for several reactions in the system CaO-Al2O3-SiO2-CO2-H2O have been calculated from the reactions calcite+quartz=wollastonite+CO2 (5) and calcite+Al2SiO5+quartz=anorthite+CO2 (19) and other published experimental studies of equilibria in the systems Al2O3-SiO2-H2O and CaO-Al2O3-SiO2-H2O.The calculations indicate that the reactions laumontite+CO2=calcite+kaolinite+2 quartz+2H2O (1) and laumontite+calcite=prehnite+quartz+3H2O+CO2 (3) in the system CaO-Al2O3-SiO2-CO2-H2O, are in equilibrium with an H2O-CO2 fluid phase having
-0.0075 for P
fluid=P
total=2000 bars.These calculations limit the stability of zeolite assemblages to low p CO2.Using the above reactions as model equilibria, several probelms of p CO2 in low grade metamorphism are discussed. (a) the problem of producing zeolitic minerals from metasedimentary assemblages of carbonate, clay mineral, quartz. (b) the significance of calcite (or aragonite) associated with zeolite (or lawsonite) in low grade metamorphism and hydrothermal alteration. (c) the reaction of zeolites (or lawsonite) with calcite (or aragonite) to produce dense Ca-Al-hydrosilicates (eg. prehnite, zoisite, grossular). 相似文献
912.
913.
914.
Seasonal patterns of microbially-mediated nitrogen cycling via the nitrification-denitrification pathway were compared between a natural and a restored salt marsh. Sedimentary denitrification rates, measured with a modification of the acetylene block technique, were approximately 44 times greater in the natural marsh relative to an adjacent transplanted marsh. Nitrification rates were similar at both sites. The difference in denitrification rates was attributed to oxygen inhibition at low tide and tidal flushing of porewater nutrients at high tide in the coarse sediments of the restored marsh. Denitrification was positively correlated with nitrification throughout the year in the natural marsh with a seasonal fall peak in denitrification corresponding to a maximum in porewater ammonia concentration. A weak correlation existed between the two processes in the restored marsh, where nitrification rates exceeded denitrification rates by a factor of 20. Transplanted marsh denitrification rates exhibited a spring peak, corresponding to elevated porewater ammonia concentrations. Our findings demonstrate functional differences in microbial nitrogen dynamics of a young (0–3 yr) restored marsh relative to a mature (>50 yr) salt-marsh system. *** DIRECT SUPPORT *** A01BY070 00008 相似文献
915.
Thompson Mary Anne Lindsay Jan M. Wilson Thomas M. Biass Sebastien Sandri Laura 《Natural Hazards》2017,86(1):31-56
Natural Hazards - Quantitatively assessing long-term volcanic risk can be challenging due to the many variables associated with volcanic hazard and vulnerability. This study presents a structured... 相似文献
916.
W. J. Chaplin J. Christensen-Dalsgaard Y. Elsworth R. Howe G. R. Isaak R. M. Larsen R. New J. Schou M. J. Thompson S. Tomczyk 《Monthly notices of the Royal Astronomical Society》1999,308(2):405-414
Determination of the rotation of the solar core requires very accurate data on splittings for the low-degree modes which penetrate to the core, as well as for modes of higher degree to suppress the contributions from the rest of the Sun to the splittings of the low-degree modes. Here we combine low-degree data based on 32 months of observations with the BiSON network and data from the LOWL instrument. The data are analysed with a technique that specifically aims at obtaining an inference of rotation that is localized to the core. Our analysis provides what we believe is the most stringent constraint to date on the rotation of the deep solar interior. 相似文献
917.
Intrusion-related gold deposits associated with tungsten-tin provinces 总被引:22,自引:0,他引:22
J. F. H. Thompson R. H. Sillitoe T. Baker J. R. Lang J. K. Mortensen 《Mineralium Deposita》1999,34(4):323-334
An under-recognized and economically important class of intrusion-related gold deposits, which occur within magmatic provinces
best known for tungsten and/or tin mineralization, is described with reference to seven major deposits (Fort Knox, Mokrsko,
Salave, Vasilkovskoe, Timbarra, Kidston and Kori Kollo). These gold deposits contain a metal suite that includes some combination
of bismuth, tungsten, arsenic, tin, molybdenum, tellurium and antimony, and contrasts with that found in the more widely-developed
gold-rich porphyry copper and related deposits. The gold deposits associated with tungsten and/or tin provinces are located
in cratonic margins, in a landward or back-arc position relative to continental margin arcs (where recognized), or within
continental collisional settings. The deposits are related genetically to felsic domes, stocks or plutons of intermediate
oxidation state, both magnetite- and ilmenite-series magmas are represented. The intrusion-hosted gold deposits are most commonly
of sheeted vein/veinlet type, although greisen-like, disseminated and breccia deposits are also described. Gold may also be
concentrated more distally (1–3 km) with respect to the intrusions, where deposits may be of skarn, disseminated replacement
or vein types. K-feldspar, albite and/or sericitic alteration assemblages, commonly including carbonate, accompany the gold
mineralization. In sheeted vein deposits, alteration is normally restricted to narrow envelopes around veins, whereas more
pervasive alteration occurs in greisen-like, disseminated and shallow (<3 km) deposits. The gold mineralization is commonly
present with low total sulphide contents (<3%), mainly pyrite and lesser arsenopyrite. In several deposits, bismuth minerals
are closely associated with gold, and bismuth-gold and tellurium-gold correlations exist. Most deposits contain tungsten,
tin, molybdenum and antimony, although generally these do not correlate with gold; tungsten and molybdenum concentrations
may increase with depth or may occur in separate zones. Base metals generally are present in minor amounts (e.g. <100 ppm
Cu). The distinct spatial association with felsic intrusions, combined with the consistent metal signature, suggests a magmatic-hydrothermal
origin. Fluid inclusions studies indicate the presence of high-salinity fluids in some deposits, and low-salinity and carbonic
fluids in most deposits, similar to the composition of fluids in intrusion-related tungsten deposits. Variations in mineralization
style largely reflect depth of formation and location relative to the intrusive centre. Several deposits in this class contain
>100 tonnes (3 million oz) of gold, thereby highlighting the gold potential of intrusion-related deposits beyond the more
traditionally explored gold and copper provinces in arc terranes.
Received: 13 March 1998 / Accepted 14 January 1999 相似文献
918.
The observed splittings of solar oscillation frequencies can be utilized to study possible large-scale magnetic fields present
in the solar interior. Using the GONG data on frequency splittings an attempt is made to infer the strength of magnetic fields
inside the Sun. 相似文献
919.
Assessing Methane in Shallow Groundwater in Unconventional Oil and Gas Play Areas,Eastern Kentucky
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Junfeng Zhu Thomas M. Parris Charles J. Taylor Steven E. Webb Bart Davidson Richard Smath Stephen D. Richardson Lisa J. Molofsky Jenna S. Kromann Ann P. Smith 《Ground water》2018,56(3):413-424
The expanding use of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations has increased public concern about potential impacts on the environment, especially on shallow drinking water aquifers. In eastern Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Berea Sandstone and the Rogersville Shale. To assess baseline groundwater chemistry and evaluate methane detected in groundwater overlying the Berea and Rogersville plays, we sampled 51 water wells and analyzed the samples for concentrations of major cations and anions, metals, dissolved methane, and other light hydrocarbon gases. In addition, the stable carbon and hydrogen isotopic composition of methane (δ13C‐CH4 and δ2H‐CH4) was analyzed for samples with methane concentration exceeding 1 mg/L. Our study indicates that methane is a relatively common constituent in shallow groundwater in eastern Kentucky, where methane was detected in 78% of the sampled wells (40 of 51 wells) with 51% of wells (26 of 51 wells) exhibiting methane concentrations above 1 mg/L. The δ13C‐CH4 and δ2H‐CH4 ranged from ?84.0‰ to ?58.3‰ and from ?246.5‰ to ?146.0‰, respectively. Isotopic analysis indicated that dissolved methane was primarily microbial in origin formed through CO2 reduction pathway. Results from this study provide a first assessment of methane in the shallow aquifers in the Berea and Rogersville play areas and can be used as a reference to evaluate potential impacts of future horizontal drilling and hydraulic fracturing activities on groundwater quality in the region. 相似文献
920.
Julian R. Thompson Honeyeh Iravani Hannah M. Clilverd Carl D. Sayer Catherine M. Heppell Jan C. Axmacher 《水文科学杂志》2017,62(15):2482-2510
Thirty UK Climate Projections 2009 (UKCP09) scenarios are simulated using a MIKE SHE/MIKE 11 model of a restored floodplain in eastern England. Annual precipitation exhibits uncertainty in direction of change. Extreme changes (10 and 90% probability) range between ?27 and +30%. The central probability projects small declines (4%). Wetter winters and drier summers predominate. Potential evapotranspiration increases for most scenarios (annual range of change: ?41 to +2%). Declines in mean discharge predominate (range: ?41 to +25%). Reductions of 11–17% are projected for the central probability. High and low flows, and the frequency of bankfull discharge exceedence reduce in most cases. Duration of winter high floodplain water tables declines. Summer water tables are on average at least 0.11 and 0.18 m lower for the 2050s and 2080s, respectively. Flood extent declines in most scenarios. Drier conditions will likely induce ecological responses including impacts on floodplain vegetation. 相似文献